cancel navigation to certain web pages

Hi,

I am developing a wpf application using web browser controls in it. Application goes like this.

1. I have a window1 with frame, whose source is page1, embedded in the window1.
2. page1 has web browser that loads www.yahoo.com and i can access other webpages of yahoo.com except certain such as mail.yahoo.com, facebook.com(certain links available on yahoo.com).

my question is how do i cancel/block access to certain links on the webpage(not the entire website) ?

Radha